During the combustion stage of the air-fuel mixture within an internal combustion engine, exhaust gases are created that exit the engine via the exhaust manifold during engine operation. However, not all gases exit the engine at this time. Some of these gases are forced to bypass the piston and enter the crankcase because of the pressure created during combustion of the air-fuel mixture.
Relief of these collected gases is necessary to avoid damage to engine gaskets caused by the extra crankcase pressure. Such damage resulted in oil leakage. An early and direct solution to the build-up of exhaust gases in the crankcase was simply to exhaust the collected gases directly to the atmosphere via, for example, a road draft tube. However, this is an undesirable solution to the presence of these gases due to the negative environmental impact generated by these unburned hydrocarbon emissions.
As an alternative, these gases can be re-introduced into the engine by evacuating them from the crankcase and adding them to the air-fuel mixture entering the engine via the intake manifold. Oil separators are known for this purpose.
A common solution to separating oil from air includes the use of a mesh filter in which oil droplets are trapped in the mesh (typically composed of a microfiber) and air is allowed to pass through. Another simple approach to separating oil from air is to provide a tube through which passes the recycled gas. The tube has holes formed on its side. Air passes through the holes and oil droplets, being heavier, fall to the bottom of a reservoir. A moving unit, such as a centrifuge, may also be used to separate oil from the air. The separated oil is directed back into the crankcase.
A very typical solution has been to have the crankcase gases flow from the crankcase to the intake manifold by way of a positive crankcase ventilation (“PCV”) system as regulated by a valve located along the PCV path. According to one PCV example, the path for the PCV begins at the valve cover and ends at the intake manifold. During engine operation, the PCV valve increases a restriction between the intake system and the crankcase in periods of higher intake manifold vacuum, thus reducing the restriction between the intake manifold and the crankcase during periods of lower intake manifold vacuum. According to this system, a slight vacuum is maintained in the engine crankcase thereby drawing hydrocarbons from the engine crankcase and directing them into the engine intake system.
It is a challenge for current gasoline engines with PCV systems to provide a significant amount of fresh air into the crankcase at high engine load conditions. With the automotive industry shift to downsize engines in heavier vehicles, engines could spend more time at higher engine load conditions during road load speeds for a significant amount of time. The PCV system has a null to insignificant amount of fresh air that enters the crankcase at higher engine load conditions. A certain ratio of fresh air-to-engine blow-by is required to prevent the acceleration of engine oil degradation which will turn the engine oil to sludge. Accelerated engine oil degradation reduces engine oil life which increases the oil change frequency requirement for the vehicle owner. If the manufacture-recommended engine oil change frequency is not followed, then the engine oil will turn to sludge and cause damage to the engine.
Accordingly, as in so many areas of vehicle technology, there is room for improvement related to the use and operation of positive crankcase ventilation systems associated with the internal combustion engine.